The invention relates to printing with a multi-segment print head and in particular to the application of dither.
A range of printer types have evolved wherein an image is constructed from ink selectively applied to a page in dot format. In U.S. Pat. No. 6,045,710 titled xe2x80x98Self-aligned construction and manufacturing process for monolithic printheadsxe2x80x99 to the inventor Kia Silverbrook there is set out an assessment of the prior art to drop on demand printers along with its manufacturing process.
Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending U.S. patent applications filed by the applicant or assignee of the present invention on May 23, 2000:
Ser. Nos. 09/575,197, 09/575,195, 09/575,159,
09/575,132, 09/575,123, 09/575,148,
09/575,130, 09/575,165, 09/575,153,
09/575,118, 09/575,131, 09/575,116,
09/575,144, 09/575,139, 09/575,186,
09/575,185, 09/575,191, 09/575,145,
09/575,192, 09/575,181, 09/575,193,
09/575,156, 09/575,183, 09/575,160,
09/575,150, 09/575,169, 09/575,184,
09/575,128, 09/575,180, 09/575,149,
09/575,179, 09/575,133, 09/575,143,
09/575,187, 09/575,155, 09/575,196,
09/575,198, 09/575,178, 09/575,164,
09/575,146, 09/575,174, 09/575,163,
09/575,168, 09/575,154, 09/575,129,
09/575,124, 09/575,188, 09/575,189,
09/575,162, 09/575,172, 09/575,170,
09/575,171, 09/575,161, 09/575,141,
09/575,125, 09/575,142, 09/575,140,
09/575,190, 09/575,138, 09/575,126,
09/575,127, 09/575,158, 09/575,117,
09/575,147, 09/575,152, 09/575,176,
09/575,115, 09/575,114, 09/575,113,
09/575,112, 09/575,111, 09/575,108,
09/575,109, 09/575,110.
In addition, various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending U.S. patent applications filed simultaneously by the applicant or assignee of the present invention: Ser. Nos. 09/607,985, 09/607,990, 09/606,999.
The disclosures of these co-pending applications are incorporated herein by cross-reference.
Of particular note are co-pending U.S. patent applications Ser. Nos. 09/575,152, 09/575,141, 09/575,125, 09/575,176, 09/575,147, which describe a microelectomechanical drop on demand printhead hereafter referred to as a Memjet printhead.
The Memjet printhead is developed from printhead segments that are capable of producing, for example, 1600 dpi bi-level dots of liquid ink across the full width of a page. Dots are easily produced in isolation, allowing dispersed-dot dithering to be exploited to its fullest. Color planes might be printed in perfect registration, allowing ideal dot-on-dot printing. The printhead enables high-speed printing using microelectromechanical ink drop technology.
In addition, co-pending U.S. patent applications Ser. Nos. 09/575,108, 09/575,109, 09/575,110, 09/607,985, 09/607,990 and 09/606,999 describe a print engine/controller suited to driving the above referenced page wide printhead.
The print engine/controller used to drive the printhead puts received print data to the printhead nozzles. It is known to apply dither to the data.
Of particular note is Ser. No. 09/607,985, which describes print engine/controller adaptations useful to interface multiple print engine/controller chips to a multi-segment printhead. It can be referred to for particular detail of the print engine/controller to which the dither process, and characterization vector, can be added.
In one form the invention resides in a method of preparing print data for a multi-segment printhead including:
establishing a set of dither matrices for a multi-segment printhead comprised of a plurality printhead chips with end portions overlapped the set consisting of a lead-in dither matrix associated with a lead in overlap portion, a lead-out dither matrix associated with a lead out overlap portion and a common dither matrix associated with a central portion of the printhead chip;
receiving print data; and
accessing the dither matrix set and applying dither to received data as it is composited to maintain a substantially constant dot gain in the resultant image across overlap portions.
For each set of two overlapping segments the overlap is characterized in terms of a misalignment. That misalignment is used to generate lead-in lead-out dither matrices and an offset into the standard third dither matrix. The lead-in lead-out dither matrices are used in conjunction over the overlap area. One can be a fadeout and the other is then a fade-in dither matrix. They are generated so that the combination of the two dither matrices gives a constant dot gain over the overlap area.
The offset is required to locate where in the third dither matrix to go to once the fade-in is finished. The third dither matrix might be thought of as the standard dither matrix, and the other two matrices as providing a cross-fade. Of the other two, one dither matrix fades out, and the other fades in.
Because of misalignment, it is not appropriate to simply continue straight on into the standard dither matrix once you have passed the overlap. Instead it may be necessary to go to a different column of the standard dither matrix, depending on misalignment.
Thus, there are preferably at least three dither matrices. A standard one that is common across all segments for the non-overlapping bits, and a pair of dither matrices per overlap. One fades out from the common dither matrix, and the other fades into the common dither matrix. Misalignment information can be obtained from a characterization vector stored on each printhead segment. The characterization vector can also store dead nozzle data. Contone CMYK layers are composited using a dither matrix selected by a dither matrix select map. The dithered contone layer has appropriate Netpage tag data added together with the black layer over the contone layer. The composite is sent to the multi-segment printhead. The datastream is adjusted to create smooth transitions across overlapping segments and it can compensate for dead nozzles in the printhead by reference to a printhead characterization vector. The resolution of the dither matrix select map should ideally match the contone resolution.
Each printhead segment can be queried via its low speed serial bus to return a characterization vector of respective segments. The characterization vectors from multiple printhead chips can be combined to construct a nozzle defect list for the entire multi-segment printhead and allows the print engine to compensate for defective nozzles during the print. As long as the number of defective nozzles is low, the compensation can produce results indistinguishable from those of a printhead with no defective nozzles.